lib/,src/: Rework findentrances into GPX export for aven.
cope with multiple survex tarballs
lib/,survex.iss.in: Add translations for the Windows installer for
all the languages we have any translations of Survex itself for.
survex.iss.in: Newer innosetup no longer supports MinVersion.
lib/,src/: Add a format drop down to the export dialog, and only
show fields which are meaningful and supported for a particular
export format.